RFR - 8132734: java.util.jar.* changes to support multi-release jar files

[Steve Drach]

>>>> Alan’s point is that traversing using entries()/stream() always returns the versioned entries (if any) rather than all entries, thus in a sense filters.
>>>> 
>>>> My assumption was the traversal should by default be consistent with a calls to getEntry, thus:
>>>> 
>>>>  jarFile.stream().forEach(e ->  {
>>>>     JarEntry je = jarFile.getJarEntry(e.getName());
>>>>     assert e.equals(je);
>>>>  });
>>>> 
>>>> There might need to be another stream method that returns all entries.
>>>> 
>>> Right, I'm mostly just wondering if entries()/streams() should override the entries in the stream with versioned entries and filter out the META-INF/versions/ tree.
>> I don’t think so.  That kind of behavior might be difficult to understand.  Returning all the entries provides some flexibility.  One can write code like this:
>> 
>> jarfile.stream().map(JarEntry::getName).filter(s ->  !s.startsWith(“META-INF”)).map(JarFile::getJarEntry).etc
>> 
>> to get the versioned results for any version you specify when constructing the JarFile.
> 
> The current specification treats those class files under meta-inf/releases like
> kind of "metadata" of those base entries. Ideally those files should not even
> be individual "files", but part of their corresponding entries. The consumer of
> the MR-Jar should not need to be aware of these version-ed entries at all to use
> this MR-jar file to load classes/resources. From this point of view, these entries
> probably should be "invisible" from entries()/stream(), when the jar file is opened
> with "version-enabled". And all returned entries should have all their "data"
> (size, csize, timestamps, crc ...) pointed to the corresponding version-ed entries,
> withe the only exception is the "name".
> 
> On the other hand it might be desired to keep JarFile.entries()/stream() asis to
> match their "zip file" perspective, to return "all" raw entries. Then it might also
> be desired to have an alternative "versioned streamVersion()" …

It seems to that we have two reasonable alternatives: (1) return all entries, and (2) return all entries except those under the “META-INF/versions/“ directory and for any entries returned, return their versioned equivalent if it exists.  If we choose alternative 2, we can still get alternative 1 by asking for JarFile.super.entries() and JarFile.super.stream().

Or we can do it both ways, leaving entries()/stream() as is and adding two new methods, versionedEntries() and versionedStream().

> 
> something like
> 
>    public Stream<JarEntry> stream(Release r); ?

We should not parametrize the methods with a Release, because what does it mean if we construct the JarFile with one Release but specify a different Release for the stream argument.  Parameterizing methods with a Release object feels like we’re starting to slide down a slippery slope.

I think adding the two new methods is the “right” solution, but I’d like some consensus here.

> 
> -sherman
> 
> 
> 
> 
>>> If I've gone to trouble of specifying the a Release then it seems the right thing to do. On the other hand, it comes at a cost and there will be use-cases like "get the names of all entries" that would be more efficient to just build on the current entries()/stream(). I'm loath to suggest this might need a new method but it might be one of the options to consider here. Minimally there is a javadoc to specify on how these methods behave when the JAR is multi-release and opened by specifying a release.
>> How’s this?
>> 
>> diff -r 68867430065b src/java.base/share/classes/java/util/jar/JarFile.java
>> --- a/src/java.base/share/classes/java/util/jar/JarFile.java	Fri Jan 29 12:34:44 2016 -0800
>> +++ b/src/java.base/share/classes/java/util/jar/JarFile.java	Mon Feb 01 09:48:05 2016 -0800
>> @@ -576,9 +576,11 @@
>>      }
>> 
>>      /**
>> -     * Returns an enumeration of the jar file entries.
>> +     * Returns an enumeration of all the jar file entries.  Constructing this
>> +     * JarFile with the {@link JarFile#JarFile(File, boolean, int, Release)}
>> +     * constructor does not modify the behavior of this method.
>>       *
>> -     * @return an enumeration of the jar file entries
>> +     * @return an enumeration of the all jar file entries
>>       * @throws IllegalStateException
>>       *         may be thrown if the jar file has been closed
>>       */
>> @@ -587,11 +589,13 @@
>>      }
>> 
>>      /**
>> -     * Returns an ordered {@code Stream} over the jar file entries.
>> +     * Returns an ordered {@code Stream} over all the jar file entries.
>>       * Entries appear in the {@code Stream} in the order they appear in
>> -     * the central directory of the jar file.
>> +     * the central directory of the jar file.  Constructing this
>> +     * JarFile with the {@link JarFile#JarFile(File, boolean, int, Release)}
>> +     * constructor does not modify the behavior of this method.
>>       *
>> -     * @return an ordered {@code Stream} of entries in this jar file
>> +     * @return an ordered {@code Stream} of all entries in this jar file
>>       * @throws IllegalStateException if the jar file has been closed
>>       * @since 1.8
>>       */